Linear motion guide unit

The present invention relates to a linear motion guide unit applicable to robots, semiconductor manufacturing apparatus, machine tools and the like, and provided with lubricating means easy of mounting to the unit.

The recently remarkable development in mechatronics technology requires linear motion guide units improved in precision, speed and miniature and the use of such apparatus extends into many technical fields. The linear motion guide units are in general employed in semiconductor manufacturing apparatus, measuring instruments, industrial robots and the like. For instance, the robots for assembling are now manufactured in various types on from a large scale to a miniature in accordance with the expansion of their usage. The linear motion guide unitsto be incorporated in such assembling robots become required to meet with needs of self-lubrication as well ashigh precision, high speed and miniature.

A conventional linear motion guide unit, as shown in FIG.10, has a sliding element, or slider 1, saddling on a track rail 2 so as to freely move along and with respect to the track rail by virtue of circulation of rolling elements 7, along the raceway grooves 4 on the rail 2. The track rail 2 has on lengthwise side surfaces 3 thereof with raceway grooves 4 and has on lengthwise upper surface thereof 14 with openings 13 spaced from each other. The track rail 2 is to befixed to a mounting base 20 such as beds, platforms, workingtables or the like. The track rail 2 is fixed together with the mounting base 20 by screwing bolts through the openings 13 of the track rail 2 and openings in the mounting base 20.

The slider 1 has a casing 5 movable with respect to the track rail 2, and end caps 6 attached to the opposing ends of the casing 5. Provided on the upper surface of the casing 5 are openings for fixture, by which other appliances, parts, chucks, grasping jaws or the like. Both of casing 5 and theend caps 6 are formed on the lower surfaces thereof with recesses 10 by which the casing 5 and end caps 6 may saddle on track rail 2 for free movement. The recesses 10 are each formed with a raceway groove 9 in opposition to any one ofthe raceway grooves 4 on the track rail 2. The rolling elements, or balls 7, are confined for free movement in raceways defined by the raceway grooves 4 and 9. Retainer bands 18 are provided in the casing 5 so as to surround balls 7 to thereby prevent the balls 7 from falling out of the casing 5. Bottom seals 8 are secured to the lower surfaces of the slider 1 for sealing between the track rail 2 and the slider 1.

The end caps 6 are provided with claws for scooping up the balls 7 from the raceway grooves 4 forming the loaded track regions with the track rail 2. The end caps have direction-changing passages for circulating movement of the balls 7. Mounted on the end caps 6 are end seals 17 for keeping sealing function between the track rail 2 and the lengthwise opposing ends of slider 2. The end caps 6 are secured to the opposing ends of the casing 5 by means of bolts 25 screwed into openings for fixture. The balls 7 move alone the loaded regions, that is, the raceway grooves 4 of the track rail 2 and then come in the direction changing passages in the end caps 6. The balls 7 further move to the return passages 12 which are formed in the casing 5 in parallel with the raceway grooves 9. It will be thus understood that the balls 27 may circulate though the raceways, direction changing passages and return passages 12. As a result, the slider 1 may move smoothly and relatively to the track rail 2 by the action of the movement of the balls 27 along the raceway defined by the raceway grooves 4 and 9 of the track rail 2 and slider 1. Grease nipples 11 are provided on the end caps 6 so as to bore through the end seals 17 and end caps 6 for feeding lubricating oil to the raceway grooves 4, 9 in which the balls 7 are held for free movement.

The prior sealing means for the linear motion guide unit are disclosed in Japanese Patent Application Laid-open Nos. 346919/1994, 35146/1995, 200362/1996, 247144/1996, 247145/1996 and 53637/1997.

Disclosed in Japanese Patent Application Laid-Open No. 346919/1994 is sealing means for side seal and under seal secured to the slider in the linear motion guide unit, in which seal lips made of rubber or synthetic resin are provided for closing tightly clearances between the slider and the track rail by keeping contact with the outer surfaces of the rail, the seal lips containing therein lubricant being constantly, continuously oozed from the seal lips to the locations to be lubricated.

Shown in Japanese Patent Application No. 283634/1986 is a method of producing sintered material of continuous porosity, which comprises the steps of mixing powdered polyethylene of ultrahigh molecular weight and powdered molding agent of polyolefin resin at a pre-determined ratio, and sintering the mixture to thereby produce porous sintered material having therein continuous porosity of average pore diameter of from 10 to 150 µm and average porosity of from 25 to 45% by volume.

In the prior linear motion rolling guide unit shown in FIG. 10, lubricating oil or grease is in general used as lubricant. Grease is fed from grease nipples 11 to the raceways for balls. Alternatively, lubricating oil is from the external piping through pipe joints attached to the slider. The slider conventionally has end seals for prevention against contamination by dust and other impurities, the end seals being made of core metal and rubber material such as acrylonitrile-butadiene rubber.

The linear motion guide units has recently come into common use over a wide area, under an adverse situation where it's next to impossible to feed lubricant, or under severe environmental conditions where the units may be covered with a large quantity of dust or chips and where it is difficult to control the temperature. It is thus required to provide the linear motion guide unit which is free of lubrication maintenance.

The sealing means for linear motion guide unit, disclosed in Japanese Patent Application Laid-Open No. 346919/1994, has end seals made of rubber or synthetic resin containing lubricant. Disclosed in Japanese Patent Application Laid-Open No. 200362/1996 is end seals made of polymer material containing lubricant.

Further disclosed in Japanese Patent Application Laid-Open Nos. 346919/1994, 200362/1996 and 53637/1996 is the sealing means made of lubricant-immersed polymer material which is manufactured by the steps of melting by the mixture of olefinic polymer with poly(α-olefin) oil, pouring the mixture into a mould and solidifying the molded mixture by cooling. It, however, has required complicated, advanced technical skill.

Any kind of prior linear motion guide units may be periodically supplied with grease or lubricating oil through the grease nipples or pipe joints, as far as the units are used under ordinary conditions. Whereas the guide units are apt to be short of lubricant under severe operating conditions such as in dusty environment, in high speed and continuous operation for many hours, or under adverse situations such as lubricant supply with difficulty. It is in general desirable that the guide units are indefinitely free from maintenance. In the prior linear motion guide units provided with the lubricant immersed polymer material disclosed in the citation above, they are under the restrictive standard in lubricant and thus could not manufactured freely in accordance with user's requirement as well as could not be replenished freely with lubricant. As a result, the users were unwillingly compelled to throw away the guide units after use.

An aim of the present invention is to overcome the shortcomings as described above with reference to the prior art, and to provide a linear motion guide unit having lubricating means in which any kind of lubricant may be contained and the lubricant may be replenished after being used up.

Another aim of the present invention is to provide a linear motion guide unit being capable of self-lubrication even under severe operating condition so as to be kept good in lubrication.

A further aim of the present invention is to provide lubricating means for the linear motion guide unit, which is applicable to the unit with only minor design modification.

A further aim of the present invention is to a linear motion guide unit having lubricating means which achieve long life-time by self-lubrication, improve the protection against dusty environment, operate under with maintenance-free, and are easy for production.

The present invention relates to a linear motion guide unit comprising a track rail provided at lengthwise side surfaces thereof with first raceway grooves, a sliding element movable with relative to the track rail and having second raceway grooves in opposition to the first raceway grooves, and lubricating means provided in the sliding means for lubricating the first raceway grooves of the track rail, wherein the lubricating means is composed of a case and lubricant delivery means provided to the case, and the lubricant delivery means make sliding contact with the first raceway grooves of the track rail to thereby supply the lubricant to the first raceway grooves of the track rail.

With the sliding movement of the lubricating means with respect to the track rail, the lubricant is drown out of the case in virtue of the lubricant delivery means so as to be applied to the track rail. The sliding movement of the sliding element along the lubricated track rail causes the automatic supply of the lubricant to rolling elements in the sliding element, so that the sliding element may move smoothly with respect to the track rail.

The case of the lubricating means is mounted on the sliding element so that the lubricating means is disposed for sliding movement along the track rail.

Alternatively, the case of the lubricating means may be attached to a mounting base which is secured to the sliding element movable along the track rail. Further, it will be designed that the sliding elements are secured to the mounting base so as to arrange the lubricating means between the sliding elements. Upon the mounting base moving with the sliding element, the lubricating means moves with relative to the track rail to thereby feed lubricant to the raceway grooves. Alternatively, the lubricating means may be disposed for sliding movement independently of and between the sliding elements which are arranged side by side with each other. With the sliding elements moving along the track rail and coming in abutting with any one of the sliding elements. The lubricating means moves with the sliding elements to lubricate the raceway grooves of the track rail. In any alternatives, it is preferred to remove from the sliding element an end seal thereof opposing to the lubricating means for easy delivery of lubricant into the sliding element.

The sliding element is composed of a casing provided with raceway grooves in opposition to the raceway grooves on the track rail, rolling elements movable in raceways defined by the opposing raceway grooves, and end caps and end seals disposed on the lengthwise opposing ends of the casing. Provided on the outer surface of any one of the end caps is a case of lubricating means on which any one of the end seals is secured, such that the lubricating means is sandwiched between the end cap and end seal.

Fixing of the end caps, end seals and case to the casing of the sliding element is made by screwing bolts into openings of the casing through aligned openings in the end caps, end seals and case, or through collars fitted in the openings of the case.

It is advantageous to improvement of efficiency in assembling to employ the fixing design of screwing bolts through the end caps, end seals and case, on securing the lubricating means between the end caps and end seals. The collars arranged in the openings of the case are preferable to protect the case against tightening force by the bolts. The openings for bolts are to be arranged at corners to reserve the space for lubricant as large as possible.

The case has a port which serves as a lubricant feed port and a vent hole. With the lubricant being consumed, the case may be replenished with the lubricant through the feed port. The lubricant feed port simultaneously serves as a vent hole for induction of air into the case in proportion to the consumption of lubricant to thereby eliminate the negative pressure in the case.

The delivery means for lubricant is made of porous sintered synthetic resin in which lubricant may ooze through pores to be fed to the raceway grooves.

The sintered synthetic resin is fabricated by filling a mold with fine powdered synthetic resin of a predetermined grading, selected from polyethylene of low density, high density or ultrahigh molecular weight, polypropylene, poly(methyl methacrylate) and tetrafluoroethylene, and heating the molded synthetic resin. The sintered synthetic resin has open pores of three-dimensional network structure.

The delivery means for lubricant comprises a head having a surface for sliding movement in contact with the raceway grooves of the track rail, and a leg integral with the head and extending into the case through an opening thereof. The lubricant contained in the case permeates the head through the leg extended in the case, and then oozes from the head to the raceway grooves of the track rail.

While the leg of the delivery means is held in the case against rotation, the head of the delivery means matches in its configuration with the cross-section of the raceway grooves, which will be in corresponding with the configuration of the rolling element. In case the rolling element is of a ball, the raceway groove has arced cross-section. Whereas the rolling element of a roller conforms to a rectangular cross-section of the raceway groove.

The head of the delivery means should have the outer surface of the configuration correspondent with the cross section of the raceway groove, which cross section is determined according to the configuration of the rolling element. For instance, in case the rolling element is of a ball, the delivery means has the outer surface of an are in the cross section perpendicular to the direction along the raceway groove, whereas a roller results in the outer surface of a rectangle in cross section. In an embodiment where the delivery means are provided at the ends of the sliding element in opposition to each other with respect to the sliding direction, the raceway grooves are sealed up between the heads of the delivery means. The leg of the delivery means is inserted in the case through the opening for axial movement and against rotation. The axial movement of the leg makes possible easy assembling of the delivery means with the sliding element. After assembly having completed, the head is held securely against rotation.

Elastic packing members are each provided in the opening of the case through which the leg of the delivery means is inserted in the case. The elastic members are to tightly seal up between the openings and the legs for the prevention lubricant against the leakage out of the case.

The elastic packing members are each also urge forcibly the head of the delivery means against the raceway groove of the track rail for steady feed of lubricant to the raceway groove of the track rail.

Lubricant used is ordinarily of grease or oil. The lubricant is mixed with powdered resin, powdered metal or felt to be oozed constantly through the delivery means.

According to the linear motion guide unit constructed as described above, the lubricant contained in the cases of the lubricating means fed little by little to the raceway grooves of the track rail by means of the delivery means which are provided to the cases and kept in sliding contact with the raceway grooves of the track rail.

The lubricant, having been fed to the raceway grooves, lubricates the rolling elements and the raceways defined by the raceway grooves of the track rail and sliding elements so that the sliding element may move smoothly with respect to the track rail.

The linear motion guide unit of the present invention has such advantage that the lubricant fed little by little to the raceways keeps good lubrication without fear of the lack of lubricant whereby the frictional resistance between the track rail and sliding element is steadily reduced. The combination or the lubricant with the delivery means may be designed for easy permeation of the lubricant into the delivery means of porous sintered resin in conformity of the lubricant with the sintered resin. The lubricating means has such advantages that the kind or lubricant may be selected in accordance with the user's requirements, the replenishment of lubricant is easy and it is easy in handling and in specification changes.

The lubricating means of the present invention further may be used incorporated in the conventional guide unit without substantial changes in principal specification. That is, this lubricating means may be widely applicable to the linear motion guide units having the track rail equal in the standard, because the case and the bubricating means thereof may be commonly employed even if the sliding element is different in type and size. In order to improve the self-lubrication performance of the guide units already having been under use in machining tools or the like, the lubricating means may also be mounted to the conventional guide units which have been incorporated in the machining tools because that this can be attached easily to the end of the sliding element.

Other aims and features or the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed, by way of example only, embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.

<u>In the drawings</u>:- <ul id="ul0001" list-style="none" compact="compact"><li>FIG. 1 is a side elevation view showing a preferred embodiment of a linear motion guide unit according to the present invention;</li><li>FIG. 2 is an exploded perspective view of the linear motion guide unit shown in FIG. 1;</li><li>FIG. 3 is a front elevation view or the linear motion guide unit shown in FIG. 1;</li><li>FIG. 4 is a plane view snowing an embodiment of lubricating means to be incorporated in the linear motion guide unit shown in FIG. 1;</li><li>FIG. 5 is a front elevation view of the lubricating means shown in FIG. 4;</li><li>FIG. 6 is a sectional view of the lubricating means and being taken along the line A-A of FIG. 5;</li><li>FIG. 7 is a sectional view of the lubricating means and being taken along the line B-B of FIG. 4;</li><li>FIG. 8 is a sectional view of the lubricating means and being taken along the line C-C of FIGS. 4 and 5;</li><li>FIG. 9 is a side elevation view showing another embodiment or the linear motion guide unit according to the present invention; and</li><li>FIG. 10 is a partially cutaway perspective view showing a prior linear motion guide unit.</li></ul>

Referring now in detail to the drawings, embodiments of the linear motion guide unit according to the present invention will be explained below, by way of example only, wherein like parts in each of the several figures are identified by the same reference character.

The linear motion guide unit of the preferred embodiment shown in FIGS. 1 to 3 primarily comprises a track rail 2 provided on its lengthwise opposing side surfaces 3 with raceway grooves 4, a sliding element, or a slider 1, saddling on the track rail 2 for sliding movement. It will be seen that the track rail 2 is of a rectangular configuration in cross section, wherein the lengthwise opposing side surfaces 3 are recessed at the raceway grooves 4. The slider 1 is composed of a casing 5 movable with respect to the track rail 2, and end caps 6 secured to the ends of the casing 5, which end are opposed lengthwise or along the moving direction of the slider 1.

The slider 1 is similar or identical in its structure with the slider shown in FIG. 10, except for lubricating means 15. It will be noted that the casing 5 has raceway grooves 9 in opposition to the raceway grooves 4, and rolling elements 7 are confined for free rotational movement in the space defined between the opposing raceway grooves 4 and 9. Retainer bands 18 are provided in the casing 5 so as to surround the rolling elements 7 for preventing the rolling elements from falling off the casing 5. Bottom seals 8 are provided on the lower surfaces of the end caps 6 as well as the casing 5 for sealing up the clearances between the lengthwise side surfaces 3 of the track rail 2 and both of the casing 5 and end caps 6. The slider 1 may move freely in virtue of the rolling elements 7 that move in a circulating manner along the raceway grooves 4 or the track rail 2. The rolling elements 7, running through the raceway grooves 4 of the track rail 2 under loaded situation, are introduced in direction-changing passages formed in the end caps 6 and then move return passages 12 that are formed in parallel with the raceway grooves in the casing 5. As a result, the rolling elements may move in a circulating manner. The slider 1 makes the free sliding movement relative to the track rail 2 in virtue of the rolling motion of the rolling elements between the opposed raceway grooves 4, 9 or the track rail 2 and the slider 1.

The linear motion guide unit of the present invention has such feature that lubricating means 15 are arranged on the end surfaces 16 or the end caps 6 for sliding movement along the track rail 2. Also provided on the lubricating means are end seals 17 for sliding movement relative to the track rail 2. The lubricating means 15 comprises a case 21 for containing therein lubricant such as grease, lubricating oil or the like, which is pored through a port 29 into the case 21, and a pair of lubricant delivery means inserted in the case 21 through openings opposed to the raceway grooves 4 of the track rail 2. The cases 21, as a whole, are a vessel or the gate-like configuration and thin in thickness. The case 21 may be made of any one of metals and synthetic resins. The case 21 is provided at a top wall 28a thereof with a port 29 which serves as a lubricant feed port and a vent hole. With the lubricant being consumed, the case 21 may be replenished with the lubricant through the feed port 29. The lubricant feed port 29 simultaneously serves as a vent hole for induction of air into the case 21 in proportion to the consumption of lubricant. Alternatively, the port 29 may be at a side 28b, instead of the top wall 28a.

The case 21 is reinforced at four corners 22 thereof, where openings 24 are provided for bolts 25 in order to fix the cases 21 to the end surfaces 16 or the end caps 6 that are mounted to the opposing ends or the casing 5. The end caps 6 and end seals 17, between which the cases 21 are to be sandwiched, have openings 26, 27 for the bolts 25 in alignment with the openings 24 of the case 21. It will be understood that all or the end caps 6, cases 21 and end seals 17 are integrally secured to the slider 1 in such a manner that the cases 21 are sandwiched between the end caps 6 and the end seals 17 by means or the bolts 25 which go through the openings 26, 24 and 27 of the end caps 6, cases 21 and end seals 17 and screw down to the casing 5 of the slider 1.

In case the case 21 is made of synthetic resin, it is preferred to dispose collars 23 in the openings 24 for protection the cases 21 from adverse deformation due to the tightening forces or the bolts 25, which force will be caused by screwing the bolts 25 against the slider 1. The tightening forces of the bolts 25 may be partially shared by the collars 23 disposed at the four corners of the case 21. With the slider 1 having been assembled, the cases 21 seal up openings 11a which have been provided for grease nipples in the conventional design.

Contained in the case 21 may be any one lubricant alone and mixture or lubricating oil with subsidiary material. Grease is typical of lubricant to be used alone. It is to be noted that the grease of high viscosity is undesired because or difficult permeation or the lubricant into the delivery means. It is preferred to employ the grease having the consistency no.1 and, for example, lithium grease. When the case 21 has contained therein the mixture of lubricant with subsidiary material, it is to be considered that the lubricant may flow out or the delivery means depending on particle density of lubricant. To cope with the problem, the powdered resin to be mixed with lubricant may be selected from the groups or fine grain size of 30 µm, intermediate grain size of 100 µm or coarse grain size of from 250 µm to 300 µm, as the operating condition may demand. An example or the powdered resin of fine grain size is ultrahigh molecular weight polyolefin. The lubricant mixed with the powdered resin of fine grain size may be oozed constantly through the delivery means. Alternatively, metal powder or felt may be used as the subsidiary material of this invention.

The delivery means 30 is composed of porous sintered high polymer resin. The porous sintered synthetic resin is fabricated by filling a mold with powdered low-density synthetic resin of a predetermined grading, for example, fine grain size of 30 µm or coarse grain size or from 250 µm to 300 µm, and heating the molded synthetic resin under pressure. The sintered synthetic resin has open pores or three-dimensional network structure. The lubricant contained in the porous sintered resin may ooze from the pores in the sintered resin.

The delivery means 30 for lubricant comprises a head 31 having a surface 40 for sliding movement in contact with the raceway grooves 4 or the track rail 2, and a leg 32 integral with the head 31 and extending into the cavity 41 case 21. The head 31 is of the semi-cylindrical shape in correspondence with the rolling elements, or balls 7. The lubricant or lubricating oil contained in the cavity 41 of the case 2 permeates the head 31 through the leg 32, and then oozes little by little from the head 31 to the raceway grooves 4 of the track rail 2.

The balls 7 and the raceway grooves 9 are sealed up by means of the tightly-sliding contact or the whole surface 40 of the head 31 with the raceway grooves 4. The leg 32 is of rectangular cross section. Upon assembling of the delivery means 30, or displacement of the head 31 for compensation of wear of the head 31, the leg 32 is movable in retractile direction, but retained against rotation around the length-wise axis of the leg 32. It will be thus understood that the head 31 of the delivery means 30 is kept in steady sliding contact with the raceway grooves 4 of the track rail 2.

Provided on the opposing walls 34 of the recess 33 or the case 21 are openings for accommodating the delivery means 30 therein. The openings have comprised of larger aperture 35 for receiving the heads 31 and smaller aperture 37, merging with each other through stepped potions 36. Mouthpieces 38 of elastic material such as synthetic rubber are provided over the apertures 35, 37 and the stepped portion 36. The mouthpieces 38 each have a bore 39. The leg 32 of the delivery means 30 is inserted through the bore 39 in the case 21 and immersed in lubricant. The elastic mouthpieces 38 each are to seal up the clearance between the delivery means 30 and the opening of the case 21 for prevention against the leakage of lubricant through the clearance. The mouthpieces 38 also urge elastically the heads 31 of the delivery means 31 towards the raceway grooves 4 of the track rail 2, so that the lubricant may be steadily applied to the raceway grooves 4 and the heads 31 may be forced out in compensation for wear of the sliding surfaces 40 of the heads 31.

With the slider 1 moving along the track rail 2, the lubricant, or grease, lubricating oil or oil component impregnated in powdered resin contained in the cavity 41 of the case 21, permeates through delivery means 30 and is applied to the raceway grooves 4 of the track rail 2. The lubricant applied to the raceway grooves 4 spreads over rolling elements 7 and raceway grooves 9 or the slider 1 to thereby lubricate the rolling elements 7 to make smooth the sliding movement or the slider 1 relatively to the track rail 2. The elastic mouthpieces 38 urge constantly the heads 31 of the delivery means 30 towards the raceway grooves 4 of the track rail 2 to seal up the raceway grooves 4 for the rolling elements 7. With the lubricant being consumed, the case 21 may be replenished with the lubricant through the feed port 29.

Another embodiment of the present invention shown in FIG. 9 is identical with the embodiment shown in FIGS. 1 and 2, except for the slider 1 and the case 21 of the lubricating means 15 being mounted to the mounting base 45 such as a table. Like parts in figures are identified by the same reference character and the detailed description is omitted.

Referring now to FIG. 9, the mounting base 45 is provided on its lower surface 46 with mounting jigs 47 by means of fitting means. The lubricating means 15 is secured to the mounting jigs 47 by fixing means, or bolts 25. Upon the mounting jigs 47 with the slider 1 moving along the track rail 2, the lubricating means 15 also move along the track rail 2 to thereby feed lubricant from the heads 31 of the delivery means 30 to the raceway grooves 4 of the track rail 2. In another case where a plurality of sliders 1 saddle on the track rail 2, the lubricating means 15 may be constructed so as to so move 45 along the track rail 2 independently of the mounting base 45. According to this arrangement, the slider 1 may move under favor or the slider 1 abutting against the lubricating mean 15.

Although the linear motion guide unit of the present invention has been described with reference to the preferred embodiments shown in FIGS.1 to 9, it is understood that the present disclosure of the preferred form has been changed in details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

Alternatively, washers of thin steel plate may be provided between the end cap 6 and the case 21 for prevention the end caps 6 and cases 21 from the deformation caused by the tightening force of the bolts 25. Whereas the head 31 in the embodiments shown above was of semi-cylindrical configuration, the head may be of a curved tip or a cylinder having a generating line along the axial line of the leg 32. Further, the embodiments described above had the rolling elements, or balls 7, and the raceway grooves 4 each had the arced cross section, whereas the rolling elements 7 may be rollers and the head 31 of the delivery means 30 has the surface 40 of the configuration corresponding to the rollers.

The linear motion guide unit of the present invention is suitable for the facilities where the escaped lubricant should be disposed without delay, such as clean rooms for semiconductor manufacturing machines where the operating environment should be prevented from the pollution with oil, food facilities where the oily material should be flushed away, and wood working facilities where dust absorbs oily material. The guide unit of the present invention may achieve good lubrication for long life-time with maintenance-free except the replenishment or lubricant.